1. Field of the Invention
This invention is generally related to video imaging systems and more particularly to improving the quality of images captured with a camera having optics suitable for intraoral imaging.
2. Description of Related Art
Video cameras configured for intraoral operation are used for capturing images of the inside of a patient""s mouth for diagnostic purposes and for patient education. To reduce camera manufacturing costs and complexity of operation, the optics in intraoral cameras typically have a fixed aperture. The aperture is optimized at a relatively small and fixed size for providing a suitable depth of field to obtain sharp images of inside the mouth without requiring a focusing mechanism.
A trade off for increased depth of field, however, is that the small aperture allows little light to reach the image sensor inside the camera. Consequently, intraoral cameras are typically equipped with a compact light source at the tip of the camera which is inserted into the patient""s mouth. The light source sufficiently illuminates the scene inside of the mouth to allow the capture of bright, detailed images of the teeth and gums despite the small aperture.
A problem, however, arises when an intraoral camera with a fixed aperture is moved outside the mouth to capture a xe2x80x9cheadshotxe2x80x9d or an image of the person""s smile or face. Because the camera""s optics and light source have been optimized for capturing images of close-up objects inside the mouth, images of scenes such as the patient""s smile or face that are further away from the camera optics often appear dark and less detailed than those of inside of the mouth taken with the same camera.
The headshots can be improved manually by the user if the intraoral camera has an adjustable aperture and focus or if the video monitor has a brightness control feature. Adjustable optics, however, are costly and can also be inconvenient for use with an intraoral camera that is normally covered with an antiseptic sheath. Furthermore, making manual adjustments on either the camera or the monitor each time the camera is removed from and inserted back into the mouth is a significant inconvenience for both the patient and the dentist.
Therefore, it is desirable to have a video camera system that automatically allows brighter and clearer images of the patient""s smile and face to be captured using a fixed-aperture intraoral camera.
An embodiment of the invention is directed at a method of electronic imaging using a video camera having an imager for generating imager signals representing a number of images, by processing the imager signals into a video signal having a black level and automatically changing the black level in response to changes in the brightness of the images. In a particular embodiment, the camera further comprises intraoral imaging optics having a fixed aperture.